1. Field of the Invention
The present invention relates to a composite thin-film magnetic head provided with an inductive write head element and a magnetoresistive effect (MR) read head element having a current perpendicular to plane (CPP) structure that passes a sense current in a direction perpendicular to surfaces of laminated layers, to a magnetic head assembly, and to a magnetic disk drive apparatus.
2. Description of the Related Art
Recently, in order to satisfy the demand for higher recording density and downsizing in a hard disk drive (HDD) apparatus, higher sensitivity and larger output of a thin-film magnetic head is required. Thus, improvement in performance of a general giant magnetoresistive effect (GMR) head with a GMR read head element is now strenuously proceeding, and also development of a tunnel magnetoresistive effect (TMR) head with a TMR read head element that can provide a double resistance change ratio or more with respect to the GMR head element is energetically performed.
Because of the difference in flowing directions of the sense currents, structures of these TMR head and general GMR head differ from each other. One head structure in which the sense current flows in a direction parallel with surfaces of laminated layers as in the general GMR head is called as a current in plane (CIP) structure, whereas the other head structure in which the sense current flows in a direction perpendicular to surfaces of laminated layers as in the TMR head is called as a CPP structure. In recent years, CPP-GMR heads not CIP-GMR heads are being developed.
Because the CPP structure utilizes magnetic shield layers themselves as electrodes, short-circuit or insufficient insulation between magnetic shield layers and element layer, which had been serious problem for narrowing the read gap in the CIP structure never inherently occurs. Therefore, the CPP structure lends itself to a high recording density head.
In recent, studied are CPP-GMR heads with spin valve magnetic multi-layered films including such as dual-spin valve type magnetic multi-layered films as in the case of the CIP-GMR heads.
The more miniaturization of the HDD apparatus with such composite thin-film magnetic head, however, causes a problem of crosstalk between a writing side and a reading side. Especially, more miniaturization of a magnetic head element causes an increase in density of a current flowing through the element due to a decrease in a cross section area of the element, as well as a decrease in thermal dissipation. Moreover, higher frequency for writing results in a steep change in voltage applied to the write head element. Consequently, a crosstalk occurs from the writing side to the reading side.
A technique to reduce a crosstalk between trace conductors in the writing side and in the reading side is proposed in Klaas B. Klaassen et al., “Write-to-Read Coupling”, IEEE Trans. Magn. Vol. 38, pp 61-67, January 2002, which analyzes a coupling mechanism between the trace conductors formed on a suspension. In the description, it is concluded that almost all crosstalk is caused by the coupling between the trace conductors, not by the inner coupling in the magnetic head.
The inventors of the present invention however thought that the inner coupling must have a great influence on the crosstalk between the writing and reading sides as well as the coupling between the trace conductors, and achieved analyses and investigations with respect to the crosstalk.
As a consequence of the analyses and investigations, it is appeared that parasitic capacitances between layers of the inductive write head element and the MR read head element of the composite thin-film magnetic head exerts an influence upon occurrence of the crosstalk. Particularly, in the composite thin-film magnetic head with the CPP structure read head element, because the lower and upper shield layers are used as electrodes of the read head element and thus a parasitic capacitance between the upper shield layer and the write coil becomes certainly larger than that between the lower shield layer and the write coil, a crosstalk voltage is produced across the read head element.
If the crosstalk voltage is produced, in the CPP-GMR read head element, a decrease in operating life of the read head element due to an enhancement of electromigration and a degradation of magnetic properties due to an enhancement of an interlayer diffusion of metal atoms may occur. Also, in the TMR read head element, if the crosstalk voltage is produced, the reading performance may be greatly degraded due to the decrease in the electrical resistance of the element caused by the formation of the pinholes in the barrier layer.
Furthermore, in the CPP-GMR read head element, because a considerable amount of noises entered in the substrate appear in the lower shield layer side electrode near the substrate, the difference between the noise in the lower shield layer side electrode and the noise in the upper shield layer side electrode is amplified at the preamplifier and then the amplified difference is superimposed on the reproduced signal. Therefore, the read head element with the CPP structure is vulnerable to external noises.
In order to reduce not only the crosstalk between the CPP-structure MR read head element and the write head element but also influence of the external noises, the assignee of the present invention proposed in U.S. Pat. No. 7,436,633a composite thin-film magnetic head configured such that a parasitic capacitance C4 between the substrate and the lower shield layer of the read head element is substantially equal to a parasitic capacitance C2 between the upper shield layer of the read head element and the lower magnetic pole layer of the write head element and that the substrate and the lower magnetic pole layer are at the same potential.
However, it is difficult to adjust the parasitic capacitances C4 and C2 to become equal to each other. This is because change in the thickness of the insulation layer between the substrate and the lower shield layer and also change in the thickness of the insulation layer between the upper shield layer and the lower magnetic pole layer are limited and also because the shape and size of the lower shield layer, the upper shield layer and the lower magnetic pole layer are limited to change.
More concretely, the thickness of the insulation layer between the substrate and the lower shield layer and also the thickness of the insulation layer between the upper shield layer and the lower magnetic pole layer cannot be increased from predetermined necessary values to keep good thermal dissipation efficiency for suppressing the thermal expansion of the magnetic pole layers due to produced heat during the write operations. Rather, in order to decrease the manufacturing time so as to achieve the economics of mass production, it is desired to form these insulation layers as thin as possible. Contrary to this, in order to prevent electrical breakdown due to charging up, these insulation layers should not be formed too thin. Therefore, it is quite difficult to adjust the parasitic capacitances C4 and/or C2 by controlling the thicknesses of these insulation layers.
Also, it is difficult to freely change the thickness, shape and size of the lower shield layer, the upper shield layer and the lower magnetic pole layer because they exert influence upon the external magnetic field resistance, upon the shield magnetic domain performance due to write stress, and upon the reading/writing characteristics. Therefore, it is extremely difficult to adjust the parasitic capacitances C4 and/or C2 by controlling these thickness, shape and size.